A criterion for the economics of motor vehicles is the frequency of the necessary maintenance intervals. In order to reduce costs and in view of the tendency towards long warranty periods, the trend for modern motor vehicles is towards very long maintenance intervals. For an electronically controlled spark ignition system the maintenance interval is significantly influenced by spark plug wear. The failure of a spark plug occurs in particular through electrode burn and electrode gap widening caused by pressure conditions. Said electrode burn increases significantly with the ignition energy applied per ignition process.
In order to extend the typical service life of spark plugs, e.g. in respect of a mileage of more than 100 000 km, it is known from EP 0 640 761 A2 to vary the ignition energy, i.e. the spark ignition current and the spark burn time, depending on various engine parameters so that the ignition energy is minimized in each case depending on said engine operating conditions and hence the electrode burn is reduced. The adjustment of the ignition parameter takes place by means of an engine parameter-dependent characteristic field for the known ignition system.
Because spark plugs in practice are relatively different in their ignition behavior depending on their actual condition (e.g. sooting) and the combustion processes are subject to a certain degree of random variation, the ignition energy is typically selected to be so high for known ignition systems that misfires are prevented under all conceivable boundary conditions.
The reduction of electrode burn achievable with a known ignition system is thus limited.
Accordingly, it is possible in some examples to provide a method for controlling an ignition system and an ignition system for implementing the method, with which the service life of the spark plugs can be increased further to the greatest extent without additional design effort and with the same ignition reliability.
This can be achieved by controlling the ignition system of an internal combustion engine having at least one cylinder with spark ignition, with which an ignition parameter influencing the ignition energy can be controlled, and with which a device for detection of misfires is provided, operation of the internal combustion engine in a calibration mode is provided, wherein the calibration mode comprises the following steps:                a) stepwise reduction of the ignition energy by changing the ignition parameter starting from an initial value,        b) detecting the reaching of a combustion failure limit based on the signal of the detection device and further reduction of the ignition energy if the combustion failure limit has not yet been reached, and        c) storing the ignition parameter at the point in time of reaching the combustion failure limit, in some embodiments taking into account an operating offset value.        
The method also comprises the operation of the ignition system on the basis of the stored ignition parameter when not in the calibration mode.